Comment deletion does not cascade
@Rickydito and I decided that our thread at http://www.duolingo.com/comment/153987$comment_id=908939 wasn't very useful. We attempted to remove the thread by "removing" comments, but we did that in reverse of the posting order. This resulted in only the last (leaf) comment actually being hidden. Instead, I think this action should be extended to all "removed" ancestor comments.
TL;DR: Removing a leaf comment should also hide all "removed" ancestor comments.